The present invention relates to certain triarylsulfonium salts having chemically combined sulfur or oxygen containing monovalent polyaryl radicals and photocurable compositions containing such triarylsulfonium salts.
Prior to the present invention, as shown by Crivello U.S. Pat. Nos. 4,058,401, 4,069,055 and 4,161,478, epoxy resins and other cationically polymerizable organic materials were rapidly cured under ultraviolet light with various aryl sulfonium salts, where all of the aforementioned patents are assigned to the same assignee as the present invention. Although valuable results were achieved by the use of such photocurable compositions and photoinitiators, the cure of the cationically polymerizable organic material was generally effective to a thickness of up to about 10-15 mils to a tack-free state within a period of up to about 60 seconds. Experience has shown that in certain applications, for example, encapsulation of electronic components, protective coatings, etc., and the like, deep section curing of various cationically polymerizable organic material, that is a cure of at least 20 mils, is often required. As a result, the use of the triarylsulfonium salt photoinitiators has been somewhat restricted.